What causes the northern lights?

The northern lights happen when charged particles from the Sun are guided by Earth's magnetic field toward the polar sky. High above the ground, those particles hit oxygen and nitrogen in the thin air, and the energized atoms give off colored light we see as aurora.

Green often comes from oxygen, while nitrogen can add violet or blue and very high oxygen can glow red. The shapes shift because the Sun's stream is uneven, so the sky can fold and brighten like slow curtains made of light.